In addition to the redesigned logs panel, Symfony 5.4 includes other improvements
related to the Symfony profiler.

Conditional profiling

Contributed by Kévin Dunglas
in #43138.

Symfony profiler provides an immense amount of debug information to quickly find
the cause of any problem. However, that comes at a price, because the profiler
must collect all that information while serving the request. This can slowdown
the application even for requests where you don't look at the profiler
information (which are most of them).
In Symfony 5.4 you can enable the profiler conditionally. To do that, add
these two new config options:

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# config/packages/dev/web_profiler.yaml
framework:
profiler:
collect: false
collect_parameter: 'profile'

The collect: false option disables the profiler by default and the
collect_parameter: profile option enables it for requests that include the
profile query parameter.
You can freely choose the query parameter name and you can also enable the
profiler by submitting a form field with that name (useful for POST requests)
and even a request attribute.

More security information in the profiler

Contributed by Nico Haase
and Robin Chalas
in #42800
and #42582.

First, the web debug toolbar now shows the security roles of the logged in user
(this only includes the roles assigned to the user directly, not the roles
assigned to them via the security roles inheritance):

Second, the security profiler panel includes a new tab called "Authenticators"
where you can check the security authenticators that were called during the
request:

HTML email preview

Contributed by Grégoire Pineau
in #43751.

The Symfony profiler includes an "Emails" panel where you can inspect the details
of the emails sent during the processing of the request. When the email is complex,
checking its HTML contents is not practical. In Symfony 5.4 we're improving this
panel to also preview the rendered HTML contents of the email:

Sponsor the Symfony project.